The use of sodium taurodeoxycholate for excystation of Eimeria tenella sporozoites.

As an in vitro excystor, sodium taurodeoxycholate (TDC) released 80--90% Eimeria tenella sporozites, in contrast to 0--15% excystation by six other bile salts or bile extracts, and pooled chicken bile in 90 min at 37 C with continuous agitation. Pooled chicken bile required 4 to 4 1/2 hr to excyst similar percentages of sporozoites. Prolonged incubation with other bile salts and bile extracts excysted most sporozoites, but killed them. When the incubation temperature was raised to 44 C, TDC excysted 100% of the sporozoites in 60 min. In all other bile salts or bile extracts, the percentage of excystation increased greatly at 44 C, but none equalled that of TDC. The molecular similarity of TDC to a naturally occurring bile salt of chickens is presented as an explanation for the superior performance of TDC as an excystor. Data are examined to minimize the possibility that excysting activity of TDC can be attributed to other bile salts present at impurities.